Air braking systems are currently in use on all freight cars. The primary function of a freight car air braking system is to provide a reliable means of slowing and stopping the car, and maintaining the car in a stationary position at the operator's discretion. Due to the obvious operational safety concerns inherent in the widespread use of such air braking systems, the mechanical, structural, and operational characteristics of these systems have been standardized by the Association of American Railroads (AAR) in the Manual of Standards and Recommended Practices, Section E, Parts I and II, Brakes and Brake Equipment. All freight cars used in interchange service in North America must comply with the requirements outlined in this publication. Other railroads, both domestic and international, have chosen to adopt the requirements of the AAR standards.
There is only one type of freight car air braking system used in the industry. This system is known as an "AB" equipment air braking system. While variations in the components of this system have been introduced and implemented over the 60 years since the system's development, the components in each variation have by design remained functionally interchangeable. The essential components of the system include a control valve, and a plurality of compressed air reservoirs, brake cylinders, and pipes (including flange and socket assemblies which allow the pipes to be connected to the other components of the system) . In a typical configuration, the brake cylinder line is coupled to the brake cylinder via a standard flange and socket assembly. One end of the brake cylinder pipe is welded to the assembly, and the assembly is coupled to the brake cylinder's receptor socket by two bolts which pass through the wings of the assembly. Air flow and pressure are maintained through this coupling by a center hole in the assembly which includes an O-ring in surrounding relation to the center hole to prevent air leakage. The air pressure in the freight car's main brake line is typically maintained at 90 psi. When the operator activates the braking system, the air pressure in the main brake line drops below 90 psi, signaling the control valve to direct compressed air from the reservoirs through the brake cylinder lines to the brake cylinders, which mechanically apply the wheel brakes accordingly. When the operator of the train releases the braking system, the air pressure in the main brake line returns to 90 psi, signaling the control valve to terminate the delivery of compressed air from the reservoirs, exhausting air from the brake cylinders to mechanically release the wheel brakes accordingly.
For the air braking system to operate safely and effectively, air leakage to and from the brake cylinder components must be minimal. To address the need for frequent testing of the brake cylinder system, the AAR technical committee approved, and industry regulators endorsed, industry compliance with the air brake test specifications outlined in a document entitled "Instruction Pamphlet 5039-4. Sup. 1" which was published by air brake manufacturers Westinghouse Air Brake and New York Air Brake, and subsequently issued as AAR Standard S-486 ("S-486") According to these testing specifications, the air brake system is to be checked whenever the freight car is removed from service due to an air brake system defect. The frequency with which this occurs varies, but is approximately 1.7 times per year per freight car according to industry data.
The current test procedure does not provide for direct measurement of brake cylinder pressure. In recent years, some provision has been made for determining that brake cylinder pressure is decreasing but there has been no way to readily determine if brake cylinder pressure is increasing. The AAR is currently processing changes to S-486 to call for direct measurement of brake cylinder pressure when brake related wheel damage is suspected. Present methods of obtaining this direct measurement of pressure and leakage involve disconnecting rigid steel pipes, inserting temporary pressure measuring devices, checking for leakage of these devices, checking the brake cylinder leakage, removing the temporary devices, and rechecking for leakage from the permanent pipe system. These procedures, although cumbersome, costly, and manhour intensive, will seek to address repetitive wheel damage to freight cars.
AAR data indicates that in 1996, the total number of wheel sets removed for tread defects was 133,964 sets. It is widely accepted in the industry that since this data does not account for instances when railroad yards repair their own freight cars, the actual number of sets would be approximately double this number, almost 268,000 sets. If it is assumed that the cost of replacing a tread damaged wheel set can be conservatively taken to be $1,000, then the cost to the industry is $268 million. With 1.3 million freight cars in service, this amounts to $206 per car per year as potential savings if tread defects could be totally eliminated. A further cost associated with wheel tread damage is the cost of damage to the track. Track damage costs are very difficult to estimate but some estimates are as high as the wheel removal costs.
A proposed Standard S-4020 ("S-4020") has recently been drafted by the AAR to specify the minimum functional and mechanical requirements, including the testing procedures, for AAR standard brake cylinder pressure taps for use during the S-486 testing, and the preferred locations of the pressure taps on freight cars of different design. While freight cars may have brake cylinder pressure taps of different design, all cars will soon be required to have at least one pressure tap which conforms generally to the proposed standard.
The S-4020 proposal stipulates that the brake cylinder pressure tap system must include a male quick disconnect valve located in a welded pipe fitting at the control valve pipe bracket, in the brake cylinder pipe, or in the brake cylinder itself. Each of these locations poses specific system design challenges. The proposed specification does not dictate how the male quick disconnect must be mounted in these locations, but rather, the pressure tap system design has been left to industry manufacturers.
The male quick disconnect valve must be of a non-oxidizing material (e.g., brass) that will withstand corrosion, and must be approved according to AAR test specifications. An O-ring seal to be used in this part is a nitrile compound which has a temperature rating of -65.degree. F. to 225.degree. F. The proposed standard dictates that the quick disconnect valve must be of a normally closed design and it must create an airtight seal at temperatures between -50.degree. F. and 150.degree. F. The valve must provide a brake cylinder connection to a pressure gauge when the female portion of the quick disconnect is fully mated with the valve stem. The configuration of the tap system must be such that no tools are required during the connect/disconnect process.
The S-4020 proposal also stipulates that the quick disconnect valves be able to pass three qualification tests. To pass the first test, the male and female quick disconnect valves must be able to be connected and disconnected 1,000 times while pressurized at 100 psi, without leaking at the coupling joint and at the male valve with the female valve disconnected. To pass the second test, the same valve configuration must be able to be heated to 150.+-.2.degree. F. for 24 hours at 100 psi, without leaking at the coupling joint and at the male valve with the female valve disconnected. To pass the third test, the same valve configuration must be able to be chilled to -50.+-.2.degree. F. for 24 hours at 100 psi, without leaking at the coupling joint and at the male valve with the female valve disconnected.
Additionally, the male quick disconnect valve must be able to pass a standard ANSI/ASTM B117 Salt Spray Test. After the valve has been subjected to the test's corrosive environment for 96 hours, subsequently cleaned with only a dry cloth, rag, or towel, and thereafter subjected to the third test outline above, a connection with a female valve must be made with the same ease as a new male valve not subjected to the corrosive environment.
Not only must the brake cylinder pressure tap system withstand the corrosive environment in which freight cars must necessarily function, but it must also be well-suited for access by maintenance and testing personnel. The S-4020 proposal therefore stipulates that suitable clearances around the disconnect valve must be maintained. Specifically, a 2.5 inch radius around the pressure tap must exist, with the exception of a 1.5 inch radius along one side of the pressure tap.
It should be reiterated that the S-4020 proposal does not dictate a specific system design, but rather only that an acceptable pressure tap will meet minimum operational and mechanical requirements. As such, manufacturers throughout the industry are free to develop acceptable system designs for the approved quick disconnect locations, each of which poses a unique design challenge.
Relevant prior art includes various pipe spacers and connectors, included and cited in Swivel Flanged Fitting, U.S. Pat. No. 3,498,643 (Mar. 3, 1970--expired), Pipe Spacer Used In Welding, U.S. Pat. No. 4,346,918 (Aug. 31, 1982), Pipe With Flange For Pipe Fitting, Pipe Flange Used Therewith and Method of Joining Said Pipe With Flange With Pipe, U.S. Pat. No. 5,415,443 (May 16, 1995), and Pipe Adapter Flange, U.S. Pat. No. 5,437,482 (Aug. 1, 1995). These systems are primarily used in conjunction with welding procedures, and/or are used simply to connect two or more pipes. While the present invention also serves to connect two or more pipes, this function is ancillary and is not the object of the invention. Rather, the purpose of the present invention is to provide a means for retrofitting already existing pipes in pressurized air systems with a means to quickly and easily measure the air pressure in the system. As S-486 has only recently been promulgated, none of the systems which comprise the relevant prior art serve this function.